1. Field of the Invention
The present invention relates to providing non-audible information within audio signals, and, more particularly, to providing non-audible information within audio signals for use in vehicles.
2. Description of the Related Art
It is known to use spread spectrum techniques to embed hidden data in the form of audio watermarks within audio content without the hidden data being perceivable by a listener. The modulation of the hidden data with a spread spectrum signal results in a bandwidth extension of the modulated message signal. This, in turn, yields a low power spectral density whose amplitude is lower than that of the narrow band audio signal. If the spectral levels of the message signals are kept at or below the masking threshold levels of the human auditory system, then the watermark is deemed inaudible by the human ear.
The typical payload data that can be embedded in the watermarks is on the order of 100 bits per second. While the encoder embeds the information within the audio signal, the receiver attempts to extract this information by performing a correlation operation with the spread spectrum code that was used to embed the data.
A problem is that it is difficult to employ watermarks in electrically noisy environments, such as an automobile. Ambient noise in an automobile, such as engine ignition noise or controller signals can have magnitudes nearly equal to the magnitude of the watermark. Electric and electric hybrid vehicles also produce electrical noise that may interfere with the watermark. Thus, it is difficult to separate the watermark from the noise such that the watermark can be discerned. Controller signals produced within a vehicle may include, for example, engine rpm information from the controller area network (CAN) bus signal.
Neither anticipated nor obvious in view of the prior art, however, are various methods of implementing the use of audio watermarks within an automotive environment, as described hereinbelow.